I tend to think of lifting everything.. so like others have said - chest up, hands up, thinking of shoulder blades together - I just have to be careful to remember to put my head back into my collar otherwise I end up looking like ET!
I've done some BHS exams and I'm not sure about the equivalence of BHS and ABRS exams. I would say that BHS exams might be more respected, mainly because they're generally well known - but that doesn't mean to say ABRS exams aren't respected! Maybe you could look through the syllabus etc...
We use them at work and they're very convenient! Obviously it wasn't me that bought them though so I'm not sure how much they are? But they are very practical and a lot tidier/ less smelly than other methods for soaking hay!